This invention relates generally to valves and deals more particularly with a ball valve having an improved seat assembly.
Conventional ball valves are equipped with metal valve seats which carry relatively soft face seals or inserts for sealing engagement with the metal ball. The face seal is typically an elastomer or a similar substance which is able to compensate for irregularities in the ball while at the same time minimizing frictional forces in order to avoid excessive operating torque. "Teflon" materials or other plastic substances are most often used for the face seal due to their desirable sealing characteristics and their low coefficient of friction when contacting metal. Although materials of this type function well at ambient temperatures, they lose much of their effectiveness at elevated temperatures and are thus unsatisfactory of high temperature service. Fire completely destroys face seals constructed of "Teflon" or any of the similar materials that are in widespread use. In addition, these substances are susceptible to rapid wear and other damage which decreases their useful life.
Preloading of conventional ball valve seats is normally accomplished by a spring which adds to the expense and complexity of the seat assembly and significantly increases the maintenance requirements. Further problems result from the need to seal the seat to the valve body, a function usually accomplished by an O-ring or another type of seal element. It has also been necessary to secure the face seal in place on the valve seat by means of glue, clamps or other fastening devices which further add to the complexity and assembly difficulties.